This invention relates to apparatus and a method for generating radiation images for use in radiation therapy. In particular, it relates to passive conversion of X-ray transmission images into light images. The invention also relates to the detection of such images by a cooled, solid-state camera, and to the acquisition, storage, and processing of the obtained images by a computer. The invention also relates to the generation of planar images and coordinated tomographic views; the generation of three-dimensional in-depth views; the simulation of irradiation beams and blocker silhouettes; and, to the fabrication of radiation blockers.
A variety of devices are presently used in radiation therapy procedures for producing so-called blockers (masks) of radiation-impermeable or radiation attenuating materials for masking radiation of all but specifically designated body areas. Conventionally, a patient is positioned in a radiographic simulator that produces real-time X-ray images and X-ray films. Under fluoroscopy conditions, a physician positions field-defining wires in the simulator to outline the desired target area and one or more x-ray films are exposed to show the entire field including the superposed field-defining wires. The patient is then dismissed and x-ray films are developed. Thereafter, the target area is manually marked on the film further to define the designated area for irradiation. Also compensator contours can be defined for generation of compensator filters.
A blocker pattern is then conventionally produced from a sheet of polystyrene foam material by manual tracing the target area (intended blocker) silhouette or contour marked on the x-ray film. This is performed in an apparatus that cuts a polystyrene foam block in appropriately scaled-down, silhouette outline along lines (rays) originating at the origin of radiation. The foam block is conventionally cut by a heated wire or by a milling machine. A compensator filter pattern may also be produced for use in conjunction with such a blocker pattern. Thusly obtained patterns are further utilized for the casting of blockers (masks) and compensator filters from appropriate radiation-impermeable or radiation-attenuating alloys.
A cast blocker and a compensator filter are eventually inserted and aligned in the radiation path of a radiation therapy apparatus, as for instance represented by cobalt sources or by linear accelerators and the like. Before treatment commences, a blocker is sometimes verified for its accuracy and alignment either in a radiographic simulator or in the actual radiotherapy apparatus (while the patient is aligned therein).
Such radiotherapy simulators are marketed in the U.S.A., for example, by the Varian Company, Palo Alto, Calif., under the name Varian Ximatron C-series Radiotherapy Simulators, and by the Kermath Manufacturing Corporation, Richmond, Va., under the name Kermath Radiographic Fluoroscopic Simulator. The Kermath Manufacturing Corporation also manufactures computer assisted tomographic (section scanning) apparatus. A Kermath T.O.P. 2000 System is used, for example, in radiotherapy simulation. Similarly, the Portalcast Block Casting System by Diacor, Salt Lake City, Utah, is a heated-wire, cutting apparatus for blocker patterns and casting apparatus for the casting of blockers.
Whereas prior-art systems for the provision of blockers are in many ways satisfactory, the involve procedures are relatively cumbersome, time consuming, and are subject to human error and to errors due to inaccuracies of existing equipment. For instance, the patient must make a special visit to a facility specifically only for initial determination of the radiation target area or field (after which the patient is dismissed). There is then a consequent need for processing of X-ray film and marking of target outline thereon; and, the need for subsequent cutting of the blocker pattern and casting of the actual blocker before the blocker may be verified (in advance of treatment). This requires another special visit by the patient which is time consuming and costly, and detrimental to the patient's tranquility. Moreover, the described procedure may need to be repeated, if verification shows the blocker to be inaccurate.
In view of the required steps and passage of time between steps (commonly amounting to at least several days), errors occur not only due to accuracy limitations of equipment and human failing, but also, for example, because of changes in the size, shape and position of tumors. In this respect, manual marking of target outlines on an x-ray film and the subsequent manual tracing of such outlines on a blocker pattern cutting apparatus contribute to the incidence of inaccuracies and errors.
Radiographic simulators employed in the past in procedures such as those described in the foregoing have relied upon generating X-ray transmission images of a patient's anatomy for direct viewing upon a flouroscope screen and/or by exposing photographic film thereto. In order to improve images and to reduce patient exposure to radiation, fluoroscopic screen images have been intensified in active image intensifiers and, further, video cameras and electronic image-grabbing and processing by a digital computer have been employed. Additionally, computer processing of radiation transmission image information has provided tomographic views to further improve accuracy, speed, convenience, and the like of radiographic simulation procedures.
Such improvements and prior art relating thereto have been disclosed and described in U.S. Pat. No. 5,014,290 and copending continuation-in-part application Ser. No. 554,883, filed Jul. 20, 1990.
Additionally, U.S. Pat. No. 4,872,187 discloses a system for inspection of minute defects in industrial parts. That system comprises an image intensifier, a linear image sensor of the charge storage type for providing tomographic images, and a light path change-over mechanism for introducing a two-dimensional output image of the image intensifier into an image pick-up tube to provide planar images.
Complexity of equipment, speed of operation, resolution and accuracy of obtainable images, and the like are matters that are of importance. For instance, an active image intensifier apparatus and a cathode-ray type camera necessarily involve considerable equipment complexity as well as image distortions and inaccuracies. For practical reasons of size (and cost) of active image intensifiers, thusly obtained images are limited in size to only a portion of the coverage area desired and conventionally provided by X-ray film in simulation procedures of concern here. Consequently, a number of such image portions have had to be assembled to provide images of adequate coverage. The latter clearly adversely affects speed of operation and accuracy. It also increases radiation exposure of the patient. Radiation exposure of the patient, however, needs to be kept as low as possible, yet sensitivity of image detection and resolution of obtained images are generally directly a function of the used radiation intensity.
Also, the provision of tomographic views in addition to planar images contributes significantly to the accuracy of irradiation simulation and verification procedures; and, such accuracy is enhanced if the number of correlated tomographic views is increased. However, in the past, each tomographic view has required a separate rotational scan of multiple images from different angles about a patient. Hence, the higher the number of tomographic views provided, the higher was the patient's exposure to radiation. Also, as each rotational scan requires a significant time, speed of acquisition of tomographic image information for multiple tomographic views has been correspondingly slow. Moreover, immobilization of a patient throughout multiple rotational scans is an additional problem.
In view of the foregoing, it is a feature of the present invention to provide improved apparatus and a method for providing relatively high-resolution, accurate planar and tomographic views, as well as 3-dimensional in-depth views of a patient's anatomy at relatively low radiation exposures. In this respect, radiation transmission images are passively converted to corresponding light images that are detected by a cooled planar detector array in a solid state camera. During a rotational scan about a patient at relatively low radiation exposure, the light images are then able to be grabbed and further processed by a digital computer to obtain tomographic information for the construction and simultaneous display of a plurality of different tomographic views and for the construction of 3-dimensional, in-depth views.